1. Field of the Invention
This invention relates to an apparatus for computing the recognized value of the amount of the solar radiation in an automobile air-conditioning system, which apparatus performs on the recognized value, specifically the output value to a control device of the detected amount of the solar radiation, a different computation when the amount of the solar radiation is tending to increase than when the amount is tending to decrease so that the automobile occupants are enabled to enjoy the optimum sensation of the air conditioning.
2. Description of the Prior Art
In recent years, the advent of the automation of the control of the automobile air-conditioning system has given birth to the practice of providing an automobile with an ambient air sensor and a solar radiation sensor, for example, detecting the ambient condition enveloping the automobile based on the signals issued from these sensors, and maintaining the environment inside the automobile constantly in spite of a change in the ambient condition outside the automobile.
One example of the technique aimed at attaining comfortable air conditioning of the automobile interior by the detection of the ambient condition outside the automobile with the aid of an ambient air sensor and a solar radiation sensor is disclosed in U.S. Pat. No. 4,696,167. The technique which is disclosed in this patent specification is based on the feedback control due to the deviation of the interior temperature from the target temperature and consequently is enabled to effect an estimated control for satisfying the condition of thermal equilibrium set in advance in due consideration of the ambient air temperature and the amount of solar radiation. It aims to overcome the disadvantage of the conventional automobile air-conditioning system. To be specific, this technique presumes the automobile air-conditioning system and the automobile interior and the like to be controlled by the system as constituting themselves one integral control system and adapts this integral control system to respond very stably such as to a sudden change in the amount of solar radiation or the ambient air temperature or even to a disturbance due to a sharp change in the set temperature of the automobile interior. More specifically, the technique is directed to determining the optimum amount of feedback necessary for enabling the inner air temperature to coincide with the target temperature based on the set target temperature for the automobile interior and the inner air temperature and consequently controlling the various magnitudes of the inflowing air in accordance with the amount of feedback. By this technique, therefore, the fluctuation of the inner temperature can be minimized even when there occurs an abrupt change as in the amount of solar radiation, for example.
Incidentally, in the conventional automobile air-conditioning system embracing the technique mentioned above, the components of the air-conditioning system are controlled by detecting the amount of solar radiation with a solar radiation sensor, performing an arithmetic operation of integration on the detected amount of solar radiation, adopting the result of the arithmetic operation as a recognized value, and using this recognized value as one of the elements for control.
The specific arithmetic operation for deriving the recognized value from the value detected by the solar radiation sensor is carried out roughly as follows.
The amounts of solar radiation detected continually by the solar radiation sensor are subjected to A/D conversion at fixed sampling intervals. The digitized amounts of solar radiation resulting from the A/D conversion are integrated with a fixed time constant. The amounts of solar radiation resulting from this integration are destined to serve as the recognized values. These recognized values, therefore, vary curvilinearly along the course of the sampling intervals mentioned above. These recognized values are adopted as one of the elements for the control of the air-conditioning. The operations of the components of the air-conditioning system are controlled on the basis of these controlling elements.
In the conventional automobile air-conditioning system of this nature, however, since the time constant for the computation of recognized values is uniquely set, the variation of recognized values has an invariable characteristic when the amount of solar radiation is increasing and when the amount is decreasing. The characteristic of this variation has been heretofore set so that the operations of the components of the air-conditioning system are controlled with the optimum following characteristic rather with respect to the increase in the amount of solar radiation. Thus, the air conditioning can be controlled to match the human feeling during the increase in the amount of solar radiation. There are times, however, when the air-conditioning cannot be controlled to match the human feeling during the decrease in the amount of solar radiation.
As regards the feeling caused by the air conditioning on the human, when the amount of solar radiation increases suddenly, comfortable sensation of the air conditioning is attained by effecting a fast following control of the air-conditioning system in conformity with the increase within the range in which the control system is warranted to operate stably. Conversely, when the amount of solar radiation decreases suddenly, comfortable sensation of the air conditioning is attained by not effecting a very fast following control of the air-conditioning system. This trend characterizes the control of the air-conditioning system. This characteristic concerns the human feeling of the air conditioning and, therefore, is specifically expressed in numerical values only with extreme difficulty. The inventors' experiment on the human feeling of the air conditioning by the use of an actual automobile has it ascertained to them that the sensation of discomfort can be avoided by gradually varying the control of the air-conditioning control system in conformity with the decrease in the amount of solar radiation when the amount of solar radiation suddenly decreases as when an automobile cruising under the scorching sun enters a tunnel.